222 C. E. Linebarger — Nature of Colloid Solutions. 



steadily in the manometric tube and in four days had reached 

 the height of about three yards. Having thus got an idea of 

 what osmotic pressure the solution would exert, I repeated the 

 experiment, using mercury* in the manometer. I pushed in 

 the manometer so that the mercury stood at about 40 cm . In 

 twenty-four hours, it had fallen to 25 - 3 cm , and remained at 

 this height for about four days. It then fell slowly and in 

 three weeks had fallen nearly 6 0m . In another experiment I 

 "set" the osmometer at about 15 cm , and in a day or so found 

 that the mercury had risen to 25"l cm . Taking the mean, a 

 solution of colloid tungstic acid containing 24*67 grms. to the 

 liter, exerts an osmotic pressure of 25'2 cm of mercury. The 

 temperature at the time of the readings was 17°. Applying 

 the formula for dilute solutions, pv — RT, I have T = 290°. 

 R = 84500, and, if the molecular mass of colloid tungstic acid 

 be 250, i. e., H 2 W0 4 , v = 10377, p = 2317-6 grm per cm 3 or 

 170*5 cm of mercury. But the experiment gave only an osmotic 

 pressure of 25*2 cm of mercury, which is <r77 times less than the 

 theoretical. Hence, as molecular mass varies inversely as the 

 osmotic pressure, the molecular mass of (H 2 ¥0 4 ) n must be 

 about 1693* and n nearly equal to 7. 



With sol. II, I obtained as a mean of several determinations 

 an osmotic pressure of 14n grm per cm 3 . As the pressure with 

 this solution was so feeble I used the solution itself in the 

 manometer, reckoning it as water. This pressure corresponds 

 to a molecular mass of 1718, which corresponds closely with 

 that obtained with sol. I. 



In round numbers then the molecular mass of colloidal 

 tungstic acid is about 1700 or nearly seven times 250, and the 

 colloidal molecule consists of seven simple molecules. 



All of the phenomena exhibited by colloids may be easily 

 explained on the assumption that the colloid molecule is very 

 large. A solution of a colloid does not seem to lower the 

 freezing point nor raise the boiling point because the molecular 

 mass is so great that it has but little influence. The raising of 

 the boiling point and lowering of the freezing point is a func- 

 tion of molecular mass ; the larger the molecule, the less 

 marked these properties of solutions. Colloid solutions do 

 not differ essentially from crystalloid solutions in this par- 

 ticular ; and the apparent difference is but one of degree. 

 Colloid solutions lower the freezing point and raise the boiling 

 point only a very little. A 5 per cent solution of colloidal 

 tungstic acid, for instance, would not depress the freezing point 

 more than 0*05°, a depression which could not be accurately 

 measured. I determined the freezing point of sol. I, finding 



* Tungstic acid attacks mercury so that at the surface of contact a blue zone 

 forms, which gradually spreads. Yet, I do not think that it had any influence 

 upon the osmotic pressure. 



